1. Field of the Invention
The present invention relates to an optical information recording medium wherein information is recorded utilizing holography. In particular, the present invention relates to a structure of an optical information recording medium wherein the generation of diffusive light from a reflective surface which causes various adverse effects is prevented when the reflective surface provided on the substrate of an optical information recording medium is irradiated with information light and recording/reproduction reference light.
2. Description of the Related Art
Holographic recording for recording information to a recording medium using holography is generally performed by superimposing light holding image information and reference light within the recording medium and writing the interference pattern formed at this time to the recording medium. When reproducing the recorded information, the image information is reproduced by diffraction due to the interference pattern by irradiating this recording medium with reference light.
One structure of an optical information recording medium implemented in this holographic recording is proposed in Patent Publication “Japanese Patent Laid-Open Publication No. 11-311936”, released on Nov. 9, 1999. The optical information recording medium proposed in this patent publication comprises a servo pit 3 provided on plastic or glass substrate 1, over which aluminum film or the like is deposited to form reflective layer 2, and further comprises hologram recording layer 4 composed of recording material and substrate 5 on top of this reflective layer, as shown in FIG. 1.
However, in FIG. 1, not only servo light (red) but also information light and reference light for recording used when recording and reference light for reproducing used when reproducing (all of which are green) reach reflective layer 2 by being irradiated onto the disk and thereby, is reflected and output from incident and output surface A as returning light. A portion of the light reflected from reflective layer 2 is reflected diffusely because reflective layer 2 is not completely flat. This diffused reflection light appears in reproducing light as scattering noise. This is problematic in that the reproduction image cannot be correctly detected by CMOS sensor or CCD and because it is extremely difficult to separate this noise. Because servo light is red light, it can be separated from the green light of information light and recording/reproduction reference lights, and therefore, scattering noise from reflective layer 2 becomes a problem when green light is emitted.
In addition, even when recording, there is a possibility that, when information light and recording/reproduction reference light reach reflective layer 2, are reflected and generate diffused reflection light, this diffused reflection light and the emitted recording/reproduction reference light both generate a different interference pattern. This interference pattern is unnecessary and is problematic in that not only may this become noise during reproduction but the recording medium will not be able to reach its original recording capacity. If the recording medium does not react to red, this will not affect the recording capacity of the recording medium will not be affected even if servo light is reflected slightly diffusely.